Python Dictionary Data Type

What is a Dictionary?

A dictionary in Python is a collection of key-value pairs. Each key must be unique, and it maps to a value.

Dictionaries are useful for storing data that is best represented as a mapping (like a real dictionary with words and definitions).

Examples:

student = {
    "name": "Alice",
    "age": 20,
    "grade": "A"
}

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Creating Dictionaries

empty_dict = {}
person = {"name": "Bob", "age": 25}

You can also use the dict() function:

person = dict(name="Charlie", age=30)

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Accessing Values

You can access values by their keys:

student = {"name": "Alice", "age": 20}
print(student["name"])  # "Alice"
print(student.get("age"))  # 20

If a key is missing, get() returns None (or a default value you specify):

print(student.get("grade", "Not Assigned"))  # "Not Assigned"

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Modifying Dictionaries

student = {"name": "Alice", "age": 20}

# Add new key-value pair
student["grade"] = "A"

# Update value
student["age"] = 21

print(student)  # {'name': 'Alice', 'age': 21, 'grade': 'A'}

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Removing Items

student = {"name": "Alice", "age": 20, "grade": "A"}

student.pop("grade")     # Removes 'grade'
del student["age"]       # Removes 'age'
student.clear()          # Removes everything

print(student)  # {}

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Looping Through Dictionaries

student = {"name": "Alice", "age": 20, "grade": "A"}

# Loop over keys
for key in student:
    print(key)

# Loop over values
for value in student.values():
    print(value)

# Loop over key-value pairs
for key, value in student.items():
    print(key, "→", value)

Output:

name → Alice
age → 20
grade → A

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Useful Dictionary Methods

student = {"name": "Alice", "age": 20}

print(student.keys())    # dict_keys(['name', 'age'])
print(student.values())  # dict_values(['Alice', 20])
print(student.items())   # dict_items([('name', 'Alice'), ('age', 20)])

# Update dictionary
student.update({"grade": "A", "age": 21})
print(student)  # {'name': 'Alice', 'age': 21, 'grade': 'A'}

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Nested Dictionaries

Dictionaries can hold other dictionaries:

school = {
    "student1": {"name": "Alice", "age": 20},
    "student2": {"name": "Bob", "age": 22}
}

print(school["student1"]["name"])  # "Alice"

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Summary

• Dictionaries store key-value pairs.
• Keys must be unique and immutable (strings, numbers, tuples).
• Values can be any data type.
• Support operations like adding, updating, removing, and looping.
• Great for structured data like records or JSON.

Dictionaries are one of the most powerful and flexible data types in Python!